1. Field of the Invention
The present invention relates to a radiation-curable composition which luminesces and/or fluoresces. The composition includes a cyanoacrylate component or a cyanoacrylate-containing formulation, a metallocene component, a polymerizingly effective amount of a photoinitiator to accelerate the rate of cure, and a luminescent and/or fluorescent dye.
2. Brief Description of Related Technology
Cyanoacrylates generally are quick-setting materials which cure to clear, hard glassy resins, useful as sealants, coatings, and particularly adhesives for bonding together a variety of substrates [see e.g., H. V. Coover, D. W. Dreifus and J. T. O'Connor, “Cyanoacrylate Adhesives” in Handbook of Adhesives, 27, 463–77, I. Skeist, ed., Van Nostrand Reinhold, New York, 3rd ed. (1990)].
With conventional polymerizable compositions other than those containing cyanoacrylate monomers, radiation cure generally presents certain advantages over other known cure methods. Those advantages include reduced cure time, solvent elimination (which thereby reduces environmental pollution, and conserves raw materials and energy) and inducement of low thermal stressing of substrate material. Also, room temperature radiation cure prevents degradation of certain heat sensitive polymers, which may occur during a thermal cure procedure.
Radiation-curable, resin-based compositions are legion for a variety of uses in diverse industries, such as coatings, printing, electronic, medical and general engineering. Commonly, radiation-curable compositions are used for adhesives, and in such use the resin may ordinarily be chosen from epoxy- or acrylate-based resins.
Well-known examples of radiation-curable, epoxy-based resins include cycloaliphatic and bisphenol-A epoxy resins, epoxidized novolacs and glycidyl polyethers. [See e.g., U.S. Pat. No. 4,690,957 (Fujiokau) and European Patent Publication EP 278 685.] The common cure mechanism for such radiation-curable epoxy-based compositions is reported to be cationic polymerization.
Well-known examples of radiation-curable, acrylate-based resins include those having structural backbones of urethanes, amides, imides, ethers, hydrocarbons, esters and siloxanes. [See e.g., J. G. Woods, “Radiation-Curable Adhesives” in Radiation Curing: Science and Technology, 333–98, 371, S. P. Pappas, ed., Plenum Press, New York (1992).] The common cure mechanism for such radiation-curable, acrylate-based compositions is free-radical polymerization.
European Patent Publication EP 393 407 describes a radiation-curable composition which includes a slow cure cationic polymerizable epoxide, a fast cure free radical polymerizable acrylic component and a photoinitiator. Upon exposure to radiation, the photoinitiator is said to be capable of generating a cationic species which is capable of initiating polymerization of the epoxide and a free radical species which is capable of initiating polymerization of the acrylic component. The polymerizable acrylic component includes monofunctional acrylates and acrylate esters, such as cyano-functionalized acrylates and acrylate esters, examples of which are expressed as 2-cyanoethyl acrylate (CH2═CHCOOCH2CH2CN) and 3-cyanopropyl acrylate (CH2═CHCOOCH2CH2CH2CN). (See page 5, lines 19–26.) The photoinitiator includes onium salts of Group Va, VIa and VIIa as well as iron-arene complexes, and generally metallocene salts, provided that the material chosen as the photoinitiator is said to be one which is capable of generating both a cationic species and a free radical species upon exposure to radiation. (See page 5, line 56 —page 7, line 15.)
Other reported information regarding photopolymerizable compositions includes formulations containing epoxy compounds and metal complexes, such as is disclosed in U.S. Pat. No. 5,525,698 (Böttcher) and U.S. Pat. No. 4,707,432 (Gatechair).
In D. B. Yang and C. Kutal, “Inorganic and Organometallic Photoinitiators” in Radiation Curing: Science and Technology, 21–55, S. P. Pappas, ed., Plenum Press, New York (1992), cyclopentadienyl transition metal complexes are discussed with attention paid to ferrocene and titanocene. In the absence of halogenated media, Yang and Kutal report that ferrocene is photoinert, though in the presence of such media and a vinyllic source free radical initiated polymerization may occur.
In C. Kutal, P. A. Grutsch and D. B. Yang, “A Novel Strategy for Photoinitiated Anionic Polymerization”, Macromolecules, 24, 6872–73 (1991), the authors note that ethyl cyanoacrylate is “unaffected by prolonged (24-h) irradiation with light of wavelength >350 nm” whereas in the presence of NCS−, cyanoacrylate is observed to solidify immediately, generating heat in the process. Though the NCS− was not in that case generated as a result of irradiation, it was generated from the Reineckate anion upon ligand field excitation thereof with near-ultraviolet/visible light. See also U.S. Pat. No. 5,652,280 (Kutal) 5,691,113 (Kutal) and U.S. Pat. No. 5,877,230 (Kutal).
International Patent Application PCT/US98/03819 describes photocurable compositions including a cyanoacrylate component, a metallocene component and a photoinitiator component. More specific examples of photoinitiators are claimed in U.S. Pat. No. 5,922,783 (Wojciak).
European Patent Publication No. EP 769 721 A1 describes a photocurable composition of (a) an α-cyanoacrylate and (b) a metallocene compound comprising a transition metal of group VII of the periodic table and aromatic electron system ligands selected from Π-arenes, indenyl, and η-cyclopentadienyl. The photocurable composition may further include (c) a cleavage-type photoinitiator. U.S. Pat. No. 5,814,180 (Mikuni) describes such compositions in the context of a method of bonding artificial nails. These European and U.S. patent documents show in their examples the ineffectiveness of the hydrogen abstraction type of photinitiators in photocurable cyanaocrylate compositions.
International Patent Application PCT/US00/24620 describes photocurable compositions including a cyanoacrylate component, a photoinitiated radical generating component and a photoinitiator component. These compositions are reported to cure through photo-induced free radical polymerization mechanisms.
In some instances irrespective of the chemistry used in the adhesive system, there is a tendency for adhesion failure to occur. In certain of these instances, adhesive failure may be due to improper placement by the end user of adhesive on the substrates to be bonded and/or when the end user does not know when the adhesive has fully cured.
Fluorescing agents have previously been incorporated into curable compositions to provide a non-destructive method of inspection such as identifying cured films, and ensuring proper coating of the composition on an article. These fluorescing agents are typically used in UV/VIS (ultraviolet/visible) curable compositions. Most cyanoacrylate compositions do not require actinic radiation to effect cure.
Other dyes have been incorporated into polymeric compositions generally to color the composition rather than as a cure indicator as there is no color change associated therewith.
U.S. Pat. No. 6,017,983 (Gilleo) appears to refer to the use of a diazo dye that is believed to form a salt or complex with acid anhydrides, which acts as a color indicator for particular anhydride/epoxy resin thermoset adhesives. The resulting salt or complex is reported to produce a chromophoric shift in the dye which is indicative of the amount of acid anhydride present, and hence, the degree of cure. As the epoxy resin cures, the amount of acid anhydride diminishes thus producing a color change. This system appears to be limited to acid anhydride hardeners used to cure epoxy resins.
U.S. Pat. No. 5,302,627 (Field) reports the addition of a dye to UV radiation curable silicone-containing polymeric compositions that contain photoinitiators. Upon exposure to UV radiation, the silicone-containing polymeric composition undergoes a color change indicating that the composition has cured. The dyes used include an anthraquinone dye having a Color Index Solvent Blue 104, 1-hydroxy-4-[(methylphenyl)amino]-9,10-anthracenedione, and an azo dye mixture of azo benzene azo naphthyl benzene amine alkyl/alkoxy derivatives having a Color Index Solvent Blue 99, and azo benzene azo naphthyl benzene amine alkyl derivatives having a Color Index Solvent Red 166. Large amounts of the dye, greater than 30 ppm based on the weight of the composition, are reported to inhibit cure.
And a recent publication [V. V. Jarikov and D. C. Neckers, Macromolecules, 33, 7761–64 (2000)] describes the simultaneoius anionic polymerization of methyl 2-cyanoacrylate and color formation with the anions produced by the photoheterolysis of crystal violet leuconitrile and malachite green leucohydroxide blue.
Notwithstanding the state of the technology, it would be desirable to provide a photocurable cyanoacrylate composition that has a built in method of detection or is “self-indicating” when cure has been achieved. Such a physical property enhances the opportunity for the end user to determine that the photocurable composition has been dispensed, in the appropriate amount and in the appropriate location. In addition, in the event that the luminescent dye provides the ability to show a first color in the uncured state and a second color in the cured state, this physical property would be desirable to end users to confirm visually without sophisticated equipment and testing when the composition has reached the cured state.